A wide theatrical release in the United States was canceled due to the 9/11 terrorist attacks. Although entirely coincidental, the film makes several references to terrorism in New York City, getting as specific as mentioning plane hijackings and Osama Bin Laden destroying the World Trade Center.
In real life Naomi Watts is afraid of elevators.
US remake of the Dutch horror film The Lift (1983), which was also written and directed by Dick Maas. Where The Lift (1983) was Maas' very first film as a director, The Shaft (2001) was the first American feature film that he directed.
When Jennifer and Mark find information about Gunter Steinberg on Harvard's website, his birth date reads April 15, 1951. It's also director/writer Dick Maas's birth date.
Though taking place in New York, most of the indoor filming was done in the Netherlands. Many of the bit players (especially among the pregnant women) are well-known Dutch actors. Ike Barinholtz, who made his feature debut here as Milligan's assistant, was already living in the Netherlands at the time, working with the famed comedy improve troupe "Boom Chicago" which also included comedian and future director Jordan Peele.